Re: EIGRP - Split Horizon

Sorry about that Jules! Hate to cause rather than to clear confusion.

The below quote of my earlier post was relative to a more
"traditional" (and not entirely technically correct in this particular
context!) definition of Split Horizon that a lot of us probably grew
up with. For example, check out this old Cisco EIGRP link:

http://www.cisco.com/en/US/tech/tk365/technologies_white_paper09186a0080094cb7.shtml#splithorizon

"Never advertise a route out of the interface through which you
learned it."

I think the OP was expecting that R3 and R4 would take a literal
interpretation of this and one would wind up advertising the R1 Lo0
route to the other and then the "learning router" (my term) wouldn't
be able to be advertised back in the other direction towards the
advertising router. That's not, in fact, what happens, as you point
out in your post. The rationale for my having said that in the first
place was to attempt to sum up what I believed to be the point of
confusion. And in doing so apparently generated even more! ;-)

Apologies,

Scott

On Jan 8, 2011, at 5:07 , jules NYA BAWEU wrote:

> Scott you got me all confused with this Split Horizon thing - please
> feel
> free to weight in with more details if you could. Here is my take on
> this:
> What Dave is seeing is a normal behavior of Split Horizon. R3 and R4
> would
> advertise R1's Lo0 to each other as long as those routes pertain to
> their
> path that connect them to R2 - you will only see one route in your
> routing
> table unless you have a variance set up or they are exactly equal path
> routes, but you would see all those routes in your EIGRP topology
> table. Now
> with EIGRP, they would not be able to advertise the route back to
> their
> interface that they have picked as best path direction - even though
> that
> router was learned from a different interface - in this case,
> assuming that
> R3 picked R2 as its best path, R3 would not advertise the path via
> R4 to to
> R2.
>
> My issue in your prior is: "and then the learning router would not
> advertise
> R1's Lo0 back to the other neighbor"
>
> Please correct me if I'm wrong.
>
> Thx
>
>
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Received on Sat Jan 08 2011 - 17:19:52 ART